A cavity filter, as a frequency selection means, has been widely applied to the field of communications, especially to the field of radio frequency communications. In a base station, filters are used to select communication signals and to filter out noises or interference signals out of the frequency band of the communication signals.
Cavity filters generally includes three categories. The first is a coaxial cavity filter, the second is a dielectric filter, and the third is a waveguide filter.
In terms of the coaxial cavity filter (hereinafter referred to as cavity filter), please refer to FIG. 1, which illustrates a structural diagram of a portion of a prior art cavity filter.
The cavity filter, as is shown in FIG. 1, comprises a cavity body 1, a cover plate 6, a resonance rod 2, and a tuning screw 3. A resonance cavity is formed within the cavity body 1. The resonance rod 2 is fixedly disposed on the bottom side of the cavity body 1, and a concave hole is defined in the resonance rod 2. The tuning screw 3 is mounted onto the cover plate 6 by means of a nut 4 and a washer 5, and passes through the cover plate to be inserted into the resonance cavity or into the resonance rod 2. Length of the portion of the tuning screw 3 that extends into the resonance rod 2 can be altered in order to adjust the RF parameters of the cavity filter.
Through study and practice on the prior art, inventors of the present disclosure have found that, in the prior art, certain space would be needed above the cover plate for accommodating the nut, the washer and the exposed portion of the tuning screw, which may increase the occupied space of the whole system; and that, when fitting the tuning screw, it will be needed to mount the nut and the washer so that the process is complicated and the material cost and the processing cost are relatively high.
Therefore, an innovative solution will be needed to solve the above mentioned technical problem.